272732 Nanoscale Aluminum, Silicon, and Aluminum/Silicon Mixture Formation for Use in Pyrotechnic Applications
Over the past two decades work in the area of energetic, pyrotechnic and explosive materials has focused on the use of nano-scale materials to tune their combustion characteristics. It has been shown that the addition of the metal nanoparticles to energetics can increase the burn rates and enhance detonation velocity. The combustion enthalpy (-7.4 kcal/g) and high specific surface area (>20 m2/g) of nano-scale aluminum has made this material of choice as an additive or fuel for energetic material formulations. Another nano-scale element that is of interest as an additive is silicon. Silicon has a similar energy density compared to aluminum and it is possible that nano-silicon will react as fast as aluminum without a passivation layer. Nano-scale silicon has provided similar results in energetic materials compared with aluminum and provides a material that is said to be less susceptible to aging and has a higher ignition temperature. These characteristics will provide a safer more reliable energetic composite material.
A major limiting factor for the uses of these nano-scale additives to energetic, pyrotechnic and explosive materials is the associated cost. The ability to produce nano-scale aluminum and silicon powders at a low cost can be accomplished using a wet attrition milling process. This milling process allows for the specific surface area of the nano-scale materials to be tuned from 5-26 m2/g and 21-106 m2/g for aluminum and silicon, respectively. This same technology can be used for the formation of mixtures of aluminum and silicon together with specific surface areas ranging between 35-50 m2/g for 4-6 hours of milling. The stoichiometric ratio of aluminum and silicon in these fuel composites is dependent on the desired application of the material.
The effect of the milling parameters (e.g. mill configuration, ratio of media to material, time, tip speed, and solvent) on the specific surface area and reactive metal content of the different fuel materials will be presented. The combustion characteristics of several different fuel materials will be tested in nanothermite composite materials and compared to traditional nanothermite materials.